1. Field of the Invention
The present invention relates to an injection molding machine which is suitable for injection molding relatively small articles, such as top or bottom stops of a slide fastener, buttons and buckles.
2. Description of the Prior Art
In some of conventional injection molding machines of the described type, an injection head cylinder and a clamping cylinder are operable by means of oil pressure, while in the other conventional injection molding machines, such actuator cylinders are operable by means of air pressure.
With the hydraulic actuator cylinders, because of their relatively high pressure, it is possible to smoothly inject molding material into the mold. However, the hydraulic cylinders are not suitable to on an injection molding machine for forming relatively small articles, since an oil pump, an oil tank, an oil cooler, and various other apparatus for regulating oil pressure are required, which would necessarily make the entire machine large in size.
On the other hand, the pneumatic actuator cylinders require only an air compressor, which would make the entire molding machine compact in size. However, because of the low pressure by the pneumatic actuator cylinders, it is necessary to enlarge the sprue and runner in the mold in order to facilitate the pouring of molten molding material into the mold. As a result, it takes a longer time to cool the molten molding material into a solid form, thus reducing the speed of molding. Further, enlargement of the sprue and runner increases the cost of molding material.